pub fn dp_rec_mc(mut amount: u32) -> u32 {
    let v = [1, 2, 5, 10, 20, 30, 50, 100];
    let mut n = 0;
    for i in v.iter().rev() {
        let np = amount / i;
        amount -= np * i;
        n += np;
    }
    n
}
